The term 'Presidential Thumbs-Down' refers to the power of the President of the United States to VETO a bill passed by Congress. The crossword solution for this term is 'VETO, ' which is a four-letter word. A presidential VETO is an executive action that allows the President to reject a bill passed by Congress, thereby preventing it from becoming law. This power is granted to the President by the Constitution and is an important part of the checks and balances system in the U.S. government.